Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover readOnly/openWorld, so the bar is lower, and the description adds genuinely non-obvious behavior: pagination is embedded in the payload rather than alongside it, requiring next_cursor to be followed until null. It also notes that large limits 'get trimmed anyway', disclosing a practical response-size constraint.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.